Mounting assembly

ABSTRACT

An apparatus includes an inner component, an outer component; and a tolerance ring located between the inner and outer components to provide an interference fit there between. The tolerance ring includes a strip of material having a plurality of radially extending projections. The strip of material is curved into a ring having a gap. The radially extending projections are compressible between the inner and outer components, and the stiffness of the radially extending projections varies around the circumference of the tolerance ring.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority from U.S. Provisional PatentApplication No. 61/095,841, filed Sep. 10, 2008, entitled “MountingAssembly,” naming inventor Andrew Robert Slayne, which application isincorporated by reference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to apparatus comprising mating inner andouter components, which are mounted together using a tolerance ring.

In an embodiment, the apparatus can be used for mounting an arm on abearing to form a pivot.

BACKGROUND

It is known to connect together mating inner and outer components usinga tolerance ring. For example, a tolerance ring may be sandwichedbetween a shaft that is located in a corresponding bore formed in ahousing, or it may act as a force limiter to permit torque to betransmitted between the shaft and the housing. The use of a tolerancering accommodates minor variations in the diameter of the inner andouter components without substantially affecting their interconnection.

Typically, a tolerance ring comprises a band of resilient material, e.g.a metal such as spring steel, the ends of which are brought towards oneanother to form a ring. A strip of projections extends radially from thering either outwardly or inwardly towards the centre of the ring. Theprojections can be formations, possibly regular formations, such ascorrugations, ridges, waves or fingers. The band thus comprises anunformed region from which the projections extend, e.g. in a radialdirection. There may be one or more rows of projections.

In use, the tolerance ring is located between the components, e.g. inthe annular space between the shaft and bore in the housing, such thatthe projections are compressed between the inner and outer components.Typically, all of the projections extend either outwardly or inwardly sothat one of the inner and outer component abuts projections and theother abuts the unformed region. Each projection acts as a spring andexerts a radial force against the components, thereby providing aninterference fit between them. Rotation of the inner or outer componentwill produce similar rotation in the other component as torque istransmitted by the ring. Likewise, linear movement of either componentwill produce similar linear movement in the outer component as linearforce is transmitted by the ring.

If forces (rotational or linear) are applied to one or both of the innerand outer components such that the resultant force between thecomponents is above a threshold value, the inner and outer componentscan move relative to one another, i.e. the tolerance ring permits themto slip.

Typically tolerance rings comprise a strip of resilient material that iscurved to allow the easy formation of a ring, e.g. by overlapping theends of the strip.

During assembly of apparatus with an interference fit betweencomponents, a tolerance ring is typically held stationary with respectto a first (inner or outer) component whilst a second component is movedinto mating engagement with the first component, thereby contacting andcompressing the projections of the tolerance ring to provide theinterference fit. The amount of force required to assemble the apparatusmay depend on the stiffness of the projections and the degree ofcompression required. Likewise, the load transmitted by the tolerancering in its final position and hence the amount of retention forceprovided or torque that can be transmitted may also depend on the sizeof the compression force and the stiffness and/or configuration of theprojections.

One example of the use of a tolerance ring is in a hard disk drive (HDD)pivot mount, where the tolerance ring provides axial retention between arotatable pivot shaft and an arm mounted thereon. In conventional pivotmounts, the tolerance ring provides an interference fit between the armand a bearing mounted on the shaft. Typically the bearing comprises twopairs of races which are axially separated from each other by a spacer.Since the components in pivot mounts are very small and sensitive, thebearing is often protected by a surrounding sleeve (a “sleeved pivot”).The sleeve often has the spacer machined on its inner surface. In sucharrangements the tolerance ring is sandwiched between the sleeve and thearm. Whilst sleeved pivots are less prone to damage and therefore areless likely to adversely affect hard disk drive performance, the precisemachining required to form the spacer on the inner surface of the sleeveand the desire to use less material in the manufacture of pivot mountshas led to the introduction of sleeveless pivots.

In sleeveless pivots, the outer race of each part of races is exposed,and the spacer comprises an annular band located axially (“floating”)between them. The spacer is held in place by an axial pre-loading forceexerted on the bearing. In such arrangements the tolerance ring islocated between the outer races of the bearing and the arm.

The coupling between mating components may exhibit resonant behavior,i.e. where external vibrations are amplified in the coupling. Theresonant frequency or frequencies of an assembly are important indetermining the operation of that assembly. For example, in hard diskdrive pivot mounts accurate data writing cannot take place whenresonance occurs, so it is important to know the frequency of resonance.The resonant frequency may depend on amount of compression that takesplace during installation.

SUMMARY

At its most general, the present disclosure proposes varying thestiffness of tolerance ring waves around the circumference to even outthe compression force experienced by an inner component held within thetolerance ring in use. The stiffness of the waves may provide means forcontrolling the compression force experienced by the inner component,which in turn may affect the properties of that component.

In one example, the inner component may be a bearing, e.g. a bearingmounting on a shaft forming part of a hard disk drive HDD pivot. Unevencompression forces exerted by the waves of the tolerance ring may causedistortion of the bearing. This may occur especially if the outwardfacing wall (e.g. the sleeve or outward facing wall of each race) of thebearing is thin, which is typical in small scale apparatus. Distortionof the bearing can have an effect on the resonant frequency of the pivotjoint in use, e.g. by contributing to bearing stiffness and rotationtorque profile. By evening out the compression forces experienced by thebearing, distortion can be controlled, e.g. minimized, which may providegreater control over the resonant frequency of the pivot joint in use.

In one aspect, an apparatus can comprise an inner component, an outercomponent which mates with the inner component, and a tolerance ringlocated between the inner and outer components to provide aninterference fit there between, wherein the tolerance ring comprising asplit ring having a plurality of radially extending projections whichare compressible between the inner and outer components, and in which inthe stiffness of the projections varies around the circumference of thetolerance ring.

The tolerance ring may comprise a strip of material that is curved intothe split ring configuration. The strip of material may comprise anunformed region from which all the projections extend in the samedirection, e.g. either all radially inward or all radially outward. Theprojections may be press-formed in the strip of material. With thisconfiguration the unformed surface of the tolerance ring abuts one ofthe inner and outer components, and the projections abut the other ofthe inner and outer components.

The stiffness of a projection may be a measure of the force required todeform the projection to a certain radial distance from the unformedsurface of the tolerance ring.

Each projection may be a circumferential hump which extends inwardly oroutwardly in the radial direction. Each hump has a circumferential widthwithin which it rises to and falls from a peak. There may be one or moreseries of humps, axially spaced from one another.

The stiffness of a projection may be altered by changing itscircumferential width. Increasing the width of a projection whilstmaintaining its radial height may soften the projection, i.e. decreaseits stiffness. Alternatively or additionally, the stiffness of aprojection may be altered by changing its radial height. Increasing theheight of a projection whilst maintaining its circumferential width mayharden a projection, i.e. increase its stiffness. Other methods ofaltering the stiffness of a projection can include altering the profileof the projection or altering the axial width of the projection. Varyingthe stiffness of the projections around the circumference of thetolerance ring may be achieved using any one of these techniques or bothin combination.

The variation in stiffness may provide stiffer projections at the gap inthe split ring, i.e. towards the ends of the strip of material that arecurved towards each other to form the ring. It has been found that thesince the projections at the gap are less constrained than those furtheraround the ring they tend to exert lower forces. Stiffening theprojections at the gap may enable the force exerted by the ring on theinner component to be distributed more evenly around its circumference.

The projections may include one or more edge projections locatedadjacent to the gap and a plurality of body projections around the ringbetween the edge projections associated with each side of the gap,wherein the edge projections have a higher stiffness than the bodyprojections. Other stiffness profiles may be used. For example, thestiffness of the body projections may increase gradually towards theedge projections. In the HDD environment it is preferred to use astiffness profile which provides an even force around the innercomponent. However, other environments may require different stiffnessprofiles, e.g. a stiffness profile which provides an uneven distributionof force around the circumference. By varying the stiffness of theprojections, any type of stiffness profile can be implemented in acontrollable and repeatable manner.

In another aspect, a hard disk drive pivot joint can include an armhaving a bore therein, a shaft receivable in the bore, and a tolerancering located between in the bore between the shaft and arm to provide aninterference fit there between, wherein the tolerance ring comprising asplit ring having a plurality of radially extending projections whichare compressible between the shaft and arm, and in which in thestiffness of the projections varies around the circumference of thetolerance ring.

The shaft may have a bearing mounted thereon. The projections on thetolerance ring may extend radially outwardly only such that an unformedregion abuts an outward facing surface of the bearing, and theprojections abut an inward facing surface of the arm within the bore.This configuration may permit the force transmitted through thetolerance ring to be diffused by the unformed region over the outwardfacing surface of the bearing.

Hard disk drive pivot joints are small, so the tolerance ring may have adiameter of less than 16 mm in use.

In another aspect, a pre-assembly apparatus can be used for a hard diskdrive pivot joint. The pre-assembly apparatus can comprise a tolerancering mounted on either one of an arm with a bore therein, the tolerancering being located in the bore, or a shaft receivable in a bore, thetolerance ring being located around the shaft, wherein the tolerancering comprising a split ring having a plurality of radially extendingprojections whose stiffness varies around the circumference of thetolerance ring.

In one embodiment the pre-assembly comprises a tolerance ring with onlyradially outwardly extending projections located in a bore formed in anarm. The diameter of the bore may be smaller than the rest diameter ofthe tolerance ring, whereby the tolerance ring is retainable thereinunder its own resilience. The projections may engage the inward facingsurface of the bore. A outward tapering axial edge may extend from oneor both ends of the tolerance ring to act as a guide for an innercomponent (e.g. shaft) to be inserted into the pre-assembly, i.e. intothe centre of the tolerance ring. Insertion of the inner component maydeform the tolerance ring to compress the projections and provide aninterference fit between the arm and the inner component.

In yet another aspect, tolerance ring comprising a split ring having aplurality of radially extending projections which are deformable toprovide an interference fit between an inner component and an outercomponent of the pivot, wherein the stiffness of the projections variesaround the circumference of the tolerance ring. The tolerance ring canbe used in a hard disk drive pivot joint.

The tolerance ring may have any of the features discussed above withreference to the other aspects of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 shows a plan view of a conventional hard disk drive pivot mountwhich includes a tolerance ring;

FIG. 2 shows a cross-section taken along the line X-X of the hard diskdrive pivot mount shown in FIG. 1;

FIG. 3 shows a close-up of the coupling between the arm and sleevedpivot of the hard disk drive pivot mount shown in FIG. 1;

FIG. 4 is a exaggerated scale roundness trace of a bearing in aconventional pivot joint without even force distribution;

FIG. 5 is a schematic diagram illustrating how tightly balls are held ina bearing in a conventional pivot joint without even force distribution;

FIG. 6 is a schematic diagram illustrating compression force exertedthrough projections around a tolerance ring which are compressed to thesame height for sample tolerance rings with and without projectionstiffness modification;

FIG. 7 is a plan view of a strip of material having projections formedtherein for a conventional HDD tolerance ring;

FIG. 8 is a plan view of a strip of material having projections formedtherein for an HDD tolerance ring that is an embodiment of the presentdisclosure;

FIG. 9 is a side view of a strip of material having projections formedtherein for an HDD tolerance ring that is another embodiment of thepresent disclosure;

FIG. 10 is a schematic diagram illustrating the different stiffnesscharacteristics of an edge projection and a body projection according toan embodiment of the present disclosure;

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

FIG. 1 shows a known hard disk drive pivot mount 30, which comprises anarm 32 adapted to carry read/write heads and pivot 34 which is rotatableon a bearing about a shaft. A tolerance ring (not shown in FIG. 1)provides an interference fit between the pivot 34 and the arm 32 suchthat the arm rotates with the pivot.

FIG. 2 shows a cross-section taken along the line 2-2 in FIG. 1. FIG. 2shows that the arm 32 comprises a circumferential housing 36 whichincludes a bore in which the pivot 34 is received. The pivot 34comprises a rotatable sleeve member 42 which is coupled to a shaft 38via a pair of bearings 40, 41. FIG. 2 thus shows an example of a sleevedpivot. The tolerance ring fits between the outer surface of therotatable sleeve member 42 and the inner surface of the bore formed inthe circumferential housing 36. This is shown in more detail in FIG. 3,where it can be seen that a tolerance ring 20 having waves 28substantially aligned with bearings 40, 41 is compressed between therotatable sleeve member 42 and circumferential housing 36.

In FIG. 3 it can be seen that rotatable sleeve member 42 comprises anintegral spacer element 43 which separates the bearings 40,41.

FIGS. 4, 5 and 6 help to illustrate the problem that is addressed by thepresent disclosure. FIG. 4 is a graphical representation of plan view ofa bearing wall 50 in an HDD pivot which is distorted in use by aconventional tolerance ring, i.e. a tolerance ring which has uniformprojections. The scale is exaggerated to demonstrate the effect. Acircular dotted line 52 represents the undistorted edge of the bearingwall. To give an idea of the scale of the distortion, the demarcations54 on the 0° , 90° , 180° and 270° axes are at intervals ofapproximately 3 μm. The overall diameter of a bearing is around 15 mm,so the scale of the distortion is small relative to the diameter.

FIG. 4 shows that the bearing wall is distorted such that it is pushedin further in the 0°-90° quadrant and the 180°-270° quadrant and sticksout in the 90°-180° and 270°-0° quadrants. It has been found that thesticking out in one quadrant occurs at the gap in the tolerance ring.Because the projections at the gap have more freedom of movement theyappear to exert a lower force. This freedom of movement is alsoreflected in looseness at the opposite side of the bearing because thebearing may shift towards the gap to occupy an off centre position wherethe forces through the projections adjacent the gap and opposite the gapare substantially equal. Thus, there is more play for the bearing wallat the gap and opposite the gap because the forces exerted by theprojections in these regions is less than the other quadrants. Thedifference in the compression forces leads to the bearing walldistortion. The compression across the bearing from projections at thegap in the ring is less than those which are not at the gap.

FIG. 5 is a diagram showing how the distortion of the bearing wallmanifests itself in the forces experiences by the balls held in thebearing's races, i.e. how tightly each ball is held in its race. FIG. 5shows that there is significant variation of tightness around thecircumference of the bearing. There are two tightness peaks, whichcorrespond to the two pushed in areas seen in FIG. 4. Likewise there aretwo regions of looseness. These occur at the gap of the tolerance ringand opposite the gap of the tolerance ring.

FIG. 6 is a graph showing the compression force transmitted throughtolerance ring projections that are compressed to a uniform height (inthis example 0.29 mm) around the circumference of the tolerance ring.Line 56 is a plot of values obtained from a conventional tolerance ringhaving uniform projections. The compression force rises to a peak at theprojections opposite the gap and is low at the projections adjacent tothe gap, i.e. at the projections which less constrained due to thepresence of the gap.

To reduce or minimize the distortion of the bearing wall, a tolerancering can have projections that exhibit an even compression force aroundthe circumference of the tolerance ring when compressed to a uniformheight (e.g. corresponding to a given clearance), as illustrated bydotted line 58 in FIG. 6.

To achieve the even compression force it is necessary to vary thestiffness of the tolerance ring projections. Varying the stiffnesspermits the compression force delivered by a projection to be tailoredto its location relative to the gap. To even out the compression forceshown in FIG. 6, the projections at the gap need to provide a strongercompression force for a given clearance, i.e. be stiffer, and the wavesin the centre need to provide a weaker compression force, i.e. be lessstiff.

FIG. 7 shows a strip of resilient material 60, e.g. spring steel, intowhich a two rows of projections 62 are press-formed, e.g. stamped. Thestrip 60 may be curved to form a tolerance ring by bring edges 66, 68towards one another. The top and bottom edges 64, 65 are flared outwards(i.e. in the same direction as the projections 62) to provide aninwardly tapering guide surface for the tolerance ring. FIG. 7 shows aconventional tolerance ring in that all of the projections have the samesize and shape.

FIG. 8 shows an embodiment of a strip of resilient material 70 having aplurality of projections 72 press-formed therein which, when edges 74,75 are curved towards one another so that the strip forms an annularband. The top and bottom edges 76, 77 are flared outwards as in FIG. 7.

Similarly to FIG. 7, the strip 70 in FIG. 8 has two rows of projections72. However, in this embodiment each row has three different types ofprojection. At (i.e. adjacent) the edges 74, 75 there is a set of threeedge projections 78. These projections have a narrower width (i.e.smaller circumferential extent) than but the same peak height as theprojections 62 shown in FIG. 7. This means they are stiffer, i.e.exhibit a higher compression force for a given compression distance.

Circumferentially inwards of each set of edge projections 78 there is aset of two intermediate projections 80. These projections are wider thanthe edge projections but have the same height (i.e. peak extension awayfrom the strip) and hence are less stiff than the edge projections.

Between the sets of intermediate projections 80 is a set of three bodyprojections 82. The body projections are each wider than an intermediateprojection but have the same height and hence are less stiff than theintermediate and edge projections. In this illustrated embodiment thebody projections 82 are the same size as the projections in FIG. 7. Thisneed not be the case. In fact, it may be preferred for the bodyprojections to be less stiff than conventional projections.

In an embodiment, the difference in stiffness between the edgeprojections and the body projections can be at least about 2%, such asat least about 3%, even at least about 5%. In certain embodiments, thedifference in stiffness between the edge projections and the bodyprojections can be at least about 7%, even at least about 10%. In aparticular embodiment, the stiffness of the edge projections can be notgreater than about two times the stiffness of the body projections, suchas not greater than about 1.9 times, such as not greater than about 1.8times, even not greater than about 1.7 times. Further, the stiffness ofthe edge projections can be not greater than about 1.6 times thestiffness of the body projections, even as not greater than about 1.5times.

The number and precise size of each type of projection may depend on theparticular use. For example, there may be no intermediate projections.There may be only one edge projection in each row at each edge.Moreover, the projections in each set need not be identical. Forexample, the edge projections could each increase in width towards theintermediate or body projections, e.g. to provide a smooth transitionbetween projection types. Similarly, the body projection may increase inwidth towards the centre of the strip, i.e. the location opposite thegap in use.

Although two rows of projections are illustrated, any number of rows maybe used. The different types of projections are preferably aligned inall the rows.

FIG. 9 shows a cross-section through a row of projection on a sheet ofmaterial 84 for making a tolerance ring. In this embodiment the widthsof each projection in the row is constant, but the peak extensionvaries. The relative heights of the projections are exaggerated forclarity.

Thus, at each edge 86, 87 there is an edge projection 88 which has agreater height (distance from unformed region 84) than the innerprojections. Circumferentially inwards of the edge projections 88 is aset of two intermediate projections 90 which have an intermediateheight. Between the intermediate projections there is a body projection92 which has a lower height than the intermediate and edge projections.As with FIG. 8, the number of each type of projection may be differentin other embodiments.

In practice, adjusting the stiffness profile of the projections may beachieved using a combination of the widening effect illustrated in FIG.8 and the raising of wave height illustrated in FIG. 9. Other methodsmay also be used, e.g. altering the cross section shape of theprojection by changing the angle of the slope of the hump or the like.

FIG. 10 is a graph showing stiffness profiles for an edge projection anda body projection to demonstrate how different compression forces aregenerated for the same clearance, i.e. annular gap between components.The stiffness profile 94 for the edge projection lies above thestiffness profile 95 for the body projection. In this embodiment, withinthe tolerance region 96 of typically annular clearances in HDD pivotmounts (i.e. between about 0.27 mm and about 0.31 mm) the edgeprojection exerts a force that is consistently about 50 N greater thanthe body projection.

1. An apparatus comprising: an inner component; an outer component; and a tolerance ring located between the inner and outer components to provide an interference fit there between, the tolerance ring comprising a strip of material having a plurality of radially extending projections, the strip of material being curved into a ring having a gap, the radially extending projections being compressible between the inner and outer components, the stiffness of the radially extending projections varying around the circumference of the tolerance ring.
 2. The apparatus of claim 1, wherein the strip of material includes an unformed region from which the plurality of projections extend.
 3. The apparatus of claim 1, wherein the unformed region abuts one of the inner and outer components, and the plurality of projections abut the other of the inner and outer components. 4.-9. (canceled)
 10. The apparatus of claim 1, wherein the tolerance ring includes one or more rows of radially extending projections, axially spaced from one another.
 11. The apparatus of claim 1, wherein the plurality of radially extending projections includes one or more edge projections located adjacent to the gap and a plurality of body projections located around the circumference of the ring.
 12. The apparatus of claim 11, wherein the stiffness of the edge projections is greater than the stiffness of the body projections.
 13. The apparatus of claim 12, wherein the stiffness of the body projections increases towards the edge projections.
 14. The apparatus of claim 1, wherein the tolerance ring has a stiffness profile that provides an even force around the inner component or the shaft.
 15. (canceled)
 16. The apparatus of claim 1, wherein the tolerance ring includes an outward tapering axial edge. 17.-33. (canceled)
 34. A preassembly apparatus for a hard disk drive pivot joint comprising: an arm having a bore therein or a shaft receivable in a bore; and a tolerance ring mounted either within the bore or around the shaft, the tolerance ring comprising a strip of material having a plurality of radially extending projections, the strip of material being curved into a ring having a gap, the radially extending projections being compressible between the bore and the shaft, the stiffness of the radially extending projections varying around the circumference of the tolerance ring.
 35. (canceled)
 36. The apparatus of claim 34, wherein the unformed region abuts one of bore and the shaft, and the plurality of projections abut the other of the bore and the shaft.
 37. The apparatus of claim 34, wherein the plurality of radially extending projections extend radially inward.
 38. The apparatus of claim 34, wherein the plurality of radially extending projections extend radially outward. 39.-46. (canceled)
 47. The apparatus of claim 34, wherein the tolerance ring has a stiffness profile that provides an even force around the inner component or the shaft.
 48. The apparatus of claim 34, wherein the tolerance ring has a diameter of less than 16 mm in use. 49.-50. (canceled)
 51. A tolerance ring comprising: a strip of material having a plurality of radially extending projections, the strip of material being curved into a ring having a gap, the radially extending projections being compressible between the bore and the shaft, the stiffness of the radially extending projections varying around the circumference of the tolerance ring. 52.-55. (canceled)
 56. The tolerance ring of claims 51, each radially extending projection having a circumferential width and a radial height.
 57. The tolerance ring of claim 56, wherein each of the radially extending projections includes a circumferential hump extending in the radial direction, the hump rising to and falling from a peak within the circumferential width.
 58. The tolerance ring of claim 56, the radial height of the radially extending projections varying around the circumference of the tolerance ring.
 59. The tolerance ring of claim 56, the circumferential width of the radially extending projections varying around the circumference of the tolerance ring. 60.-66. (canceled) 